The enzyme dopamine Beta-hydroxylase occupies a central role in the pathway in which tyrosine is converted to the neurotransmitter norepinephrin e. Determination of dopamine Beta-hydroxylase activity and norepinephrine levels after sucrose density gradient centrifugation, makes it possible to locate and identify specific populations of Storage granules. Experiments will be carried out to examine questions with regard to the functional role of the several populations of vesicles. These experiments will involve noradrener gic vesicles isolated from the rat heart and cerebral cortex and dopaminergic vesicles isolated from the caudate nucleus. The fraction of dopamine B-hydroxylase activity which is membrane enclosed will be determined in isolated large and small vesicles. In other experiments the turnover rates of several vesicle markers will be determined to examine the possibility that vesicles are reused. It is possible to induce synapse formation between sympathetic ganglia and the pineal organ. The effects of drugs and of changes in the media on synapse formation will be investigated. There are several factors which may potentially limit the expression of dopamine Beta-hydroxylase activity "in vivo". We will investigate the possibility that access of dopamine to the enzyme, which is sequestered in adrenergic storage vesicles, is a limiting factor in norepinephrine biosynthesis . These experiments will solve incubating isolated vesicles "in vitro" with catecholamines and with various ions and drugs. In another series of experiments we will attempt to purify an endogenous inhibitor of dopamine Beta-hydroxylase. This inhibitor has a moleclar weight of approximately 3000 and it appears to be present in adrenergic storage vesicles and in chromaffin granules. The mechanism of action of this inhibitor and its chemical structure will be determined. BIBLIOGRAPHIC REFERENCES: Molinoff, P.B., Nelson, D.L., and Harden, T.K.: Biochemical and morphological characterizations of adrenergic storage vesicles. Sixth International Congress of Pharmacology, Helsinki, Finland, Ab. 363, l975. Molinoff, P.B. and Orcutt, J.C: Access of endogeneous inhibitors of dopamine Beta-hydroxylase (DBH) tothe enzyme. Fed. Prod., 35: 929, l976.